Various refrigeration systems have been known. One such example of a refrigeration system is disclosed in Japanese Patent Application Kokai (not examined) Gazette No. 5-5567. The apparatus shown in the 5-5567 patent utilizes a binary refrigeration cycle and includes a primary refrigerant circuit through which a primary refrigerant passes and a secondary refrigerant circuit through which a secondary refrigerant passes. The exchanging of heat between the primary refrigerant and the secondary refrigerant takes place in a refrigerant heat exchanger. Such a refrigerant heat exchanger is called a cascade heat exchanger.
Some of refrigeration systems of the above-described type employ multiple secondary refrigerant circuits with respect to one primary refrigerant circuit with a view to providing a great deal of flexibility. This sole primary refrigerant circuit is shared as a source of heat among multiple heat exchangers disposed on the side where refrigerant heat is utilized.
Such a conventional refrigeration system employs a structure comprising a plurality of cooling units disposed on the indoor side. Each cooling unit is provided with an individual secondary refrigerant circuit. In other words, the primary refrigerant circuit includes liquid and gas flow lines which are branched out into liquid and gas flow branch lines. These branch lines are guided to individual cooling units. In each cooling unit, heat is exchanged between primary and secondary refrigerants in the refrigerant heat exchanger.
Each of the cooling units is arranged in series with the liquid flow line of the primary refrigerant circuit. As a result of such arrangement, the primary refrigerant passes through the cooling units in sequence. In each of the cooling units, a heat exchange takes place between primary and secondary refrigerants.